An Australian Patent Application No. 70208/81 filed by Whitco Pty. disclosed a deadlock wherein the main bolt enters the striker plate to a greater depth when the lock is in the locked position and which however has the following defects:
1. The locking tongue (21) having a single angled face (22, not double angled face) can only be provided for a single-direction door opening or closing, to thereby be inconvenient for a door system requiring a bi-directional in-and-out opening or closing operation.
2. Since the tongue (21) has a single angled face (22) and the striker plate (23) should be carefully oriented in a single direction as mounted on a door frame, adapted to receive the inclined surface of the tongue when closing a door, it is therefore inconvenient for installing such a conventional deadlock on a door and a door frame.
The present inventor has found the defects of a conventional deadlock and invented the present bi-directional deadlock.